The invention relates to a monitoring apparatus for monitoring operation of a no-back device of an actuator assembly driven by a motor.
No-back devices are known for use with motor-driven actuators for preventing external forces driving the actuator in a direction contrary to a selected direction of actuation. Such no-back devices may also counter effects of external assisting forces on the actuator, that is, forces tending to act on the actuator in the selected direction. No-back devices are particularly useful for use in safety-critical applications, for example with actuators for controlling aircraft flight control surfaces, but are not limited to such applications. The correct functioning of such no-back devices is particularly critical in the event of a mechanical, electrical or hydraulic failure in an actuator""s forward drive system, which could otherwise allow the actuator to be driven by external forces.
An example of a known linear no-back device of the screw and nut type is described in GB-A-1 309 645, although the invention also has applications for use with rotary no-back devices.
One problem encountered using known actuator assemblies, for example aircraft flight control surface actuator assemblies, is that hitherto, whilst safety checks have been routinely made for faults in the no-back devices for example excessive backlash and for wear, which could indicate a potential risk of failure of the no-back device, no means has been provided for checking the condition of a no-back device during operation of the device in an actuator assembly.
In accordance with the invention, there is provided a monitoring apparatus for monitoring operation of a no-back device of an actuator assembly driven by a motor, the apparatus comprising sensor means operable to sense an operating parameter of tie motor for determining when the motor""s output drive is in a direction opposite to a selected direction of motor output drive.
If the output drive of the motor is acting in a direction opposite to the selected direction, this implies the no-back device is in failure mode. The invention facilitates the provision under operating conditions of an immediate indication of a fault arising in a no-back device of an actuator assembly. Such active condition monitoring is particularly advantageous in safety critical actuator assemblies, for example those used to control aircraft flight control surfaces.
The sensor means may be operable to sense a direction of a current which passes through the motor. This sensor means is for use with an electric motor.
Alternatively, the sensor means may be operable to sense a direction of flow of a fluid which passes through the motor. This sensor means is for use with a fluid-powered motor, for example an hydraulic motor.
Preferably, the monitoring apparatus comprises determination means operable to determine when the motor""s output drive is in a direction opposite to the selected direction of motor output drive using information about the operating parameter sensed by the sensor means.
The detonation means may comprise a data processor and may further comprise a comparator connected to the data processor.
The monitoring apparatus may comprise indication means operable to provide an indication, for example a visual and/or audible warning signal, when the determination means has determined that the motor""s output drive is in a direction opposite to the selected direction of motor output drive, for alerting an operator of all actuator assembly that a no-back device of the actuator assembly is in failure mode.
According to a further aspect of the invention, there is provided an aircraft flight-control means comprising a flight control surface and an actuator assembly for controlling an attitude of the surface relative to a body portion of the aircraft, the actuator assembly being driven by a motor and including a no-back device, the flight control mean further comprising a monitoring apparatus as described above for monitoring operation of the no-back device.
In accordance with a further aspect of the invention, there is provided a method of monitoring operation of a no-back device of an actuator assembly driven by a motor, the method comprising sensing an operating parameter of the motor for determining when the motor""s output drive is in a direction opposite to a selected direction of motor output drive.
The method may comprise sensing a direction of a current which passes through the motor.
Alternatively, the method may comprise sensing a direction of flow of fluid which passes through the motor.
The method may comprise providing an indication, for example a visual and/or audible warning signal, when the motor""s output drive is in a direction opposite to the selected direction of motor output drive, for alerting an operator of an actuator assembly that a no-back device of the actuator assembly is in failure mode.